The invention relates to a method of adjusting the position of a micro-mechanical bi-material cantilever during manufacture. More particularly, the invention relates to implanting ions into the bi-material to modify internal stress of at least one material of the bi-material to adjust the position of the cantilever.
Ion implantation is widely utilized for controlling electrical characteristics in semiconductor devices during the impurity doping process. Ion implantation may also be utilized to reduce stress in thin films. In the semiconductor fabrication industry in particular, the importance of low stress in thin films is great as it impacts the reliability of the semiconductor device. After deposition of the film, ion implantation may be used to alter the internal stress and change the stress gradients in the conductive and/or dielectric layers of the film.
Recently, micro-mechanical bi-material cantilever sensors have been developed. These devices include a cantilever beam which bends, or deflects, when infrared radiation is absorbed by an infrared responsive absorber element of the beam. The infrared radiation heats the bi-material section of cantilever beam, thereby urging one of the bi-materials to expand at a greater rate than the other bi-material (i.e., as each material has a different thermal expansion coefficient), causing the cantilever to deflect, or bend with respect to a substrate of the sensor. The corresponding change in capacitance between the cantilever and the substrate, produces a signal that is used to measure the amount of radiation incident thereto.
The signal is detected by an arrangement of a fixed reference capacitor and the variable cantilever capacitor forming a charge divider which, when sampled, forms a voltage that is proportional to the cantilever capacitance.
Yet, difficulties have arisen in fabricating stress free layers uniformly and predictably to form the structure of the micro-mechanical bi-material cantilever sensor. The sensor""s design is based on the assumption that arrays of identical cantilevers can be formed with two thin film layers having different thermal expansion coefficients. The performance of the sensor is determined in part by the position of the cantilever beam relative to the substrate. This bi-material structure is intended to change its position as its temperature changes. However, the initial position depends upon the relative stress of the cantilever beam (and stress gradients). The thin films used are difficult to control accurately by deposition parameters, as can be appreciated, producing cantilever beam structures of uniform initial position is also difficult.
Accordingly, there is a need for a method to predictably form and/or calibrate micro-mechanical bi-material cantilever sensors such that cantilever beams can be uniformly and predictably positioned.
The present invention provides a method of adjusting the position of a micro-mechanical bi-material cantilever. The bi-material portion of the device includes a first and second material and each material has a corresponding thermal expansion coefficient. The method includes modifying internal stress of the first material relative to the second material by implanting ions to the first material. The position of the bi-material is monitored to modulate the dosage of implanted ions.
According to one aspect of the invention, a method of calibrating an array of micro-mechanical bi-material cantilever sensors with an ion beam is provided. Internal stress of at least one material of the bi-material is modified by the ion beam to adjust the position of the cantilever relative to a corresponding substrate material of each sensor of the array.
According to another aspect of the invention, a method of calibrating an array of micro-mechanical bi-material cantilever capacitive sensors with an ion beam is provided. The sensors each providing a variable capacitance formed between the cantilever and a sensor substrate. Internal stress of at least one material of the bi-material is modified by implanting ions of the ion beam into the material to adjust the position of the cantilever relative to a corresponding substrate material of each sensor for adjusting the variable capacitance of each sensor.